This invention relates generally to gas turbine engines, and more specifically to methods and apparatus for balancing an assembly that includes a gas turbine engine.
At least some known gas turbine engines include, in serial flow arrangement, a compressor, a combustor, a high pressure turbine, and a low pressure turbine. The compressor, combustor and high pressure turbine are sometimes collectively referred to as the gas generator or core engine. Compressed air is channeled from the compressor to the combustor where it is mixed with fuel and ignited. The combustion gasses are channeled to the turbines which extract energy from the combustion gasses to power the compressors and to produce useful work to propel an aircraft in flight or to power a load, such as an electrical generator.
Balancing turbine engines facilitates the avoidance of potentially destructive vibrational forces during engine operation. Balancing is achieved by rotating the assembly and determining the magnitude and location of each imbalance. Material is then added or removed to correct the unbalance. Generally, the rotating components are balanced individually, and after the components are assembled, the assembly is then balanced to correct for any cumulative unbalance in the assembly. Within at least some applications, the low pressure turbine or power turbine is coupled to other rotating components that necessitate further balancing.
Within at least some known engine assemblies, the power turbine, is coupled to a generator. When the engine is installed in a vessel, it is desirable that the engine and generator be field balanced as installed to facilitate preventing the generation of potentially damaging vibrational forces being induced to the surrounding vessel. Typically, balancing in two planes is recommended to lower the vibration to acceptable limits. In two-plane balancing of the engine and generator assembly, an aft plane of the power turbine and a second plane forward of the power turbine are typically selected as balancing planes. While the aft plane of the power turbine is usually readily accessible, access to a forward balancing plane may be less accessible. For example, in at least some engine assemblies, the front balancing plane is only accessible through drive shaft cover access ports. Moreover, in at least some engine assemblies, field balancing may require at least a partial disassembly of a bolted joint to install a balance weight under a nut or a bolt. However, disassembling such joints may actually cause another imbalance if the components are misaligned when reassembled.